1. Field of the Invention
The present invention relates to a method for manufacturing a nonreciprocal circuit device, and in particular, to a nonreciprocal circuit device, e.g., an isolator or a circulator, which is used in a microwave band and a method for manufacturing a composite electronic component including the nonreciprocal circuit device.
2. Description of the Related Art
Nonreciprocal circuit devices, e.g., isolators and circulators, have a characteristic that signals are transmitted in a predetermined specific direction and are not transmitted in the reverse direction. For example, the isolator is used in transmitting circuit portions of mobile communication equipment, e.g., automobile telephones and cellular phones, by taking advantage of this characteristic.
Generally, this type of nonreciprocal circuit device includes a ferrite-magnet device made of ferrite provided with a center electrode and a permanent magnet arranged to apply a direct current magnetic field thereto and a predetermined matching circuit device defined by a resistance and a capacitor. Furthermore, a composite electronic component including a plurality of nonreciprocal circuit devices or a composite electronic component including a nonreciprocal circuit device and a power amplifier device, for example, have been provided as modules.
The above-described ferrite-magnet device is typically bonded (for example, via reflow soldering) to a surface of a substrate after the magnetic force of the permanent magnet is measured and adjusted (see, for example, Japanese Unexamined Patent Application Publication No. 2002-299914 and Japanese Unexamined Patent Application Publication No. 2005-117500). Therefore, a leakage magnetic flux of the permanent magnet which has already been magnetized tends to attract or repel other devices which are bonded to the surface of the substrate at the same time and which have magnetic portions. Consequently, a large distance is required between the ferrite-magnet device and other devices. Thus, there is a problem in that the size of a nonreciprocal circuit device or a composite electronic component provided with the ferrite-magnet device is large, and cannot be sufficiently reduced.